1. Field of the Invention
The present invention is related to an apparatus for preventing explosive vapors contained in a sewer from being transmitted to the atmosphere surrounding the sewer. More particularly, the present invention relates to apparatuses for insertion into existing sewer inlets commonly covered by gratings or other sewer covers which prevent explosive vapors contained in the sewer from being ignited by sparks or flames in the atmosphere on the outside of the sewer.
2. Description of the Prior Art
Industries which manufacture and process flammable liquids and gases such as hydrocarbons have difficulty in keeping the hydrocarbons and other flammable liquids from finding their way into the sewer system located beneath the manufacturing facility. Flammable liquids and gases which enter such sewer systems can be easily ignited by welding or cutting operations occurring in the vicinity of the inlets to the sewer system.
Such problems are commonly encountered in the petroleum refining industry. In most petroleum refining facilities elaborate systems are used to recover hydrocarbons in the sewer system for processing into useful product.
Hydrocarbons and other flammable liquids and gases are ever present in the sewer systems of petroleium refiners, and precautions must be taken when performing burning and welding in the facility of sewer inlets. Commonly, the sewer inlet is covered with a vinyl coated canvas having a border filled with sand or sawdust to prevent flammable gases in the sewer from being ignited by burning or welding operations in the refinery. The vinyl cover has a reservoir to retain water which adds weight to the interior of the cover to improve the seal over the inlet. The area immediately surrounding a sewer inlet may be gravel or dirt, but in most cases the surrounding area is either asphalt or concrete.
When the area surrounding a sewer cover is asphalt or concrete it is extremely difficult to seal the perimeter of the sewer cover, even using a vinyl coated canvas cover filled with water, sand and/or sawdust. In addition to placing the sewer cover over the inlet or man way and filling it with water, sand must be placed around the outside of the border to aid in sealing the sewer inlet from the surrounding area. Such a seal is necessary to prevent flammable gases from escaping from the sewer inlet and to keep sparks from burning and welding operations from entering the sewer system and igniting flammable gases therein.
Commonly, in a petroleum refinery while burning or welding is in progress, a water spray is directed toward the sparks generated by the burning and welding to cool the metal being welded or cut and to cool any molten pieces of metal falling from the work area. Canvas blankets are sometimes placed around the site of the burning or welding while the burning or welding is in progress, and a water spray is directed to the exterior of the canvas blankets to prevent sparks from entering the sewer and coming into contact with flammable liquids or gases in the sewer.
Such measures provide minimal protection from explosion and/or fires in the sewer systems of petroleium refiners and other chemical processing plants. The perimeter of the sewer cover even when covered with sand may still allow flammable gases and hot sparks to come into contact with each other, even though canvas blankets may be placed around the site of the cutting or welding.
U.S. Pat. No. 4,305,679 discloses a man hole sealing device to prevent water from entering a man hole through the corbel joint between the man hole casing and the cover frame. The cover disclosed completely seals a man hole. Such a device would not be pertinent to the present invention in which water flow into a sewer is permitted rather than completely stopped.
U.S. Pat. No. 4,045,346 discloses a basement sewer trap comprising a coupling sleeve for a sewer pipe having an interior cup or well, the interior of the cup supporting a funnel tube beneath a water strainer. The water flows through the strainer, down through the funnel tube, upward out of the cup portion, and finally down the open end of the coupling sleeve into a sewer pipe.
U.S. Pat. No. 3,621,623 discloses an apparatus for temporarily closing an opening formed at the top of a vertical wall of a catch basin, man hole or the like, the man hole arrangement employing a trough type member 32 having a removable lid 31 as disclosed in FIG. 6. However, the lid completely closes the man hole and does not allow any flow therethrough, whereas in the present invention it is necessary to have fluid flow through the sewer cover.
U.S. Pat. No. 3,516,541 discloses a drain device comprising a prefabricated structure that may be removably mounted in a vertical drain structure which when partially filled with water provides a seal to prevent upward discharge of explosive vapors through the drain structure into the ambient atmosphere. The structure disclosed therein comprises a first cylinder open at the top and bottom contained within a second outer cylinder having a series of holes therein through which water flowing downwardly through the first cylinder and outwardly from the bottom of the first cylinder may exit.
U.S. Pat. No. 129,246 discloses a cover "E" which is placed on the cap ring of the mouth of a water pipe gate and two other covers "GG" which are placed over pyramidal or conical sections to form a dead air space therebetween.